Beginner Exercise 170 / Solution

Black lives (most likely)  

After , White has two options - the first is to allow a life for the top half and capture 10 stones in sente.

White opts for ko  

The second is this ko for the whole group. But Black takes first and there would be no matching ko threats for such a huge ko (about 50 points worth) in most cases. So the above diagram is the most likely result.

( at a is slightly better for points, but it gives Black a ko threat at to live the top half)

Probe ( to elsewhere)  

(For advanced readers) In rare cases, here may work as a probe. White must play if he wants to kill the whole group. Then Black plays elsewhere to change the ko threat situation, and if successful plays cut. Then lives with two more points and destroys one point for White at a.